feat: playwright browser cache mount + PLAYWRIGHT_BROWSERS_PATH; ops guide: MCP stack inherited from base image

docker/ops-context/AGENTS.md

@@ -41,7 +41,12 @@ When asked to prepare a workspace for a repo (e.g. "prepare empstream"):
 
    Include everything an agent working in that repo needs (compilers, DB
    clients, protobuf, etc.). The base already has: node 24, pi, golang, git,
-   ripgrep, make, jq, gopls. Don't reinstall those.
+   ripgrep, make, jq, gopls, **the MCP stack (cloakbrowser-mcp, playwright
+   via npx, chromium runtime libs, `/root/.config/mcp/mcp.json`)** plus
+   shared browser-cache mounts (`/cloakbrowser-cache`, `/pw-browsers`).
+   Don't reinstall any of those — `FROM lvmh-worker:latest` inherits them.
+   If a repo needs an extra MCP server, MERGE it into the image's
+   `/root/.config/mcp/mcp.json` (never overwrite the existing servers).
 
 3. **Build**: